1. Field
The present invention pertains to prosthetic dentistry and more particularly, to a simple and convenient single mounting pin as well as a means for casting a base and dental model with a removal die all in a single operation.
2. Prior Art
A typical assembly for prosthetic dentistry is shown in FIG. 1. This assembly comprises a base 101 with an opening 107, a model 102 secured to the base, a die 103 which is removably attached to said base and a mounting pin 105 secured to the die.
As can be seen in FIG. 1, a replica of the tooth to be reproduced, referred to as the die 103, is made so that it may be removed from the base 101. The removable feature facilitates fabrication of the selected tooth from the die. The die is formed at the same time as the replica of the adjoining teeth, assuring a proper fit with respect to these teeth.
Since the replica of the adjoining teeth, referred to as the dental mode 102, are permanently attached to the base, the pin must align the die with the base and simultaneously with the replica of the adjoining teeth. This alignment is usually accomplished by casting the die about the pin and then in a separate operation, casting the base about the remainder of the pin. These two casting operations may take up to 45 minutes each. It would be preferable if both could be accomplished at the same time. The need for the double casting operation is due to the fact that in conventional systems some means is necessary to support the pin while the casting material sets about that portion of the pin which is within the die. This means of temporarily supporting the pin is removed and then the base is cast.
The die is cast using a mold which is a negative impression of a denture, such as that shown in FIG. 2. In this Figure, a pin 105 is held in place in a negative impression 201. This impression is designed to accept, in the area about the pin, a suitable casting material such as gypsum to form the die with a portion of the pin secured within it.
After the casting material in the die has set, the support means for the pin in a conventional system is removed and the base is poured in a separate, second operation.
In some instances a plastic sleeve is used to cover the portion of the pin which is to be embedded in the base so that after relieving and cleaving the die, the pin may be removed from the base without difficulty.
The usual relieving and cleaving procedures carried out after the die, model and base have hardened consist of cutting through the casting material on either side of the die to carry out the relieving operation. The cleaving operation is carried out by cutting the material across the bottom of the die. This allows the die to be separated from the model and base. The lines along which these operations are carried out is shown in FIG. 3, wherein a dental model 304 is shown to include a die 305 with an integral alignment pin 306. The die is relieved along lines 301 and 302 and cleaved along line 303.
A number of different shaped pins are currently in use. The most commonly used pins are shown in FIGS. 4 through 8. FIG. 4A shows the side view of a first pin 401, while FIG. 4B shows a cross sectional view of this pin. The flat leading edge 402 is intended to prevent this pin from rotating in the base, but, unfortunately, the trailing edge 403 is round and the result is the pin tends to break the gypsum after a few insertions and rotate in the opening in the base.
FIG. 5 shows a second type of pin and its associated sleeve. FIG. 5A shows a side view of this pin, while FIG. 5B shows a cross sectional view. FIG. 5C shows a side view of a sleeve adapted to accept this pin. The pin is inserted in the sleeve and the sleeve is cast into the base. In this way, the casting material in the base is protected by the sleeve from being broken by the pin. The pin includes a flat area 501 to prevent rotation; however, the complete device including the flat area 501 is usually made so wide that it is not suitable for the smaller anterior, or front teeth.
FIG. 6 illustrates a third type of pin in which FIG. 6A is a side view of the pin, FIG. 6B is a cross sectional view of the pin and FIG. 6C shows a breakaway portion of the associated sleeve. This type of pin is completely round and therefore requires a minimum of two pins to prevent rotation of the die. In addition, carbide drills are required to produce the openings in the base to accept the sleeves. In addition, a machine is required to drill the dental model.
FIG. 7 illustrates a fourth type of pin in which FIG. 7A is a side view and FIG. 7B is a bottom view. This pin requires the stocking of three different sizes to accommodate all the various sizes of teeth.
FIG. 8 shows a mold for a fifth type of pin in which the mold 801 holds two straight pins, 802 and 803, used to secure the mold to the negative impression. The alignment pin itself is formed from the casting material, such as gypsm. It is, therefore, weak in comparison to the other pins which are metal. Unfortunately, this type of pin tends to break off from the die.
With the exception of the last mentioned molded pin, all the pins thus far described require two casting operation, which is both costly and time consuming.